Scroll type positive displacement apparatus have attracted a great deal of interest for any of a variety of reasons including theoretical simplicity, the ability to generate very high pressures or expand relatively large volumes with an apparatus that is physically quite small, and the fact that scroll type apparatus lend themselves to multi-stage configurations.
As is well known, scroll type apparatus are generally comprised of a pair of flat plates in generally parallel relation with each plate having one or more spiral vanes extending axially toward the other plate to interfit with a vane or vanes thereon. Depending upon the design, both plates may be rotated with one additionally orbiting with respect to the other or one plate may be merely orbited with respect to the other which is stationary. In either event, closed pockets defined by points of contact of the vanes travel between radially inner and radially outer locations along the interface between the plates and serve to convey fluid between ports disposed at such locations.
When used as a compressor or a pump, the radially outer port will be an inlet port, while the radially inner port, frequently formed in a shaft supporting one of the scrolls, will be an outlet port. When used as an expander, the arrangement is the reverse.
In either event, a high pressure area is disposed centrally of the plates, that is, at the radially inner port, either due to the presence of the fluid being compressed at that location or the admission of the fluid under high pressure to be expanded to a lower pressure at such location. The relatively high pressure tends to drive the plates axially apart. Should the plates move appreciably apart in the the axial direction, the ability to seal the pockets is lost as is the efficiency of operation of the apparatus.
Consequently, the prior art has proposed preloading the plates towards each other in the axial direction. However, when it is desired to start up the preloaded apparatus, the large frictional forces existing at the points of contact between the scrolls make the apparatus hard to start.
To avoid this difficulty, the prior art has proposed to the application of the high pressure at the radially inner port to the side of either or both of the scrolls opposite the interface so as to act oppositely of the high pressure at the area centrally of the interface which tends to separate the plates. In other words, existing high pressure is utilized to balance the high pressure at the interface prevents separation.
This approach, while successful, has been implemented only at the expense of complexity and bulk in terms of requiring the presence of chambers to receive the balancing pressure and direct the same against the scrolls oppositely of the interface, various seals, etc.
The present invention is directed to the provision of simplified means for preventing axial separation of the scrolls during operation in the scroll-type apparatus.